Forward Osmosis Membranes: The Significant Roles of Selective Layer

Abstract

Forward osmosis (FO) is a promising separation technology to overcome the challenges of pressure-driven membrane processes. The FO process has demonstrated profound advantages in treating feeds with high salinity and viscosity in applications such as brine treatment and food processing. This review discusses the advancement of FO membranes and the key membrane properties that are important in real applications. The membrane substrates have been the focus of the majority of FO membrane studies to reduce internal concentration polarization. However, the separation layer is critical in selecting the suitable FO membranes as the feed solute rejection and draw solute back diffusion are important considerations in designing large-scale FO processes. In this review, emphasis is placed on developing FO membrane selective layers with a high selectivity. The effects of porous FO substrates in synthesizing high-performance polyamide selective layer and strategies to overcome the substrate constraints are discussed. The role of interlayer in selective layer synthesis and the benefits of nanomaterial incorporation will also be reviewed.

Defect-Healed Carbon Nanomembranes for Enhanced Salt Separation: Scalable Synthesis and Performance

“…14,45,55 Owing to the more uniform pore size distribution in the CNM than that in NG, our composite shows a NaCl rejection of 99.8%, which is higher than all other NG-, GO-, and rGO-based composites (Figure 4c) and comparable to the commercially available CTA membrane 45 and state-of-the-art TFC membranes. 44,46,48 Interestingly, our PA/CNM/PET composite with an overall water flux of 12 LMH under FO using 1 M NaCl against DI water lies also in the flux range for TFC FO membranes. 46,48 ■ CONCLUSIONS…”

“…In terms of material properties, the high nanopore density of CNMs (∼10 18 m –2 ) allows a comparable water permeance as nanoporous atomically thin graphene membranes on the micrometer scale. As a consequence, our PA/CNM/PET composites show a water flux comparable to those nanoporous graphene (NG) composites. ,, Owing to the more uniform pore size distribution in the CNM than that in NG, our composite shows a NaCl rejection of 99.8%, which is higher than all other NG-, GO-, and rGO-based composites (Figure c) and comparable to the commercially available CTA membrane and state-of-the-art TFC membranes. ,, Interestingly, our PA/CNM/PET composite with an overall water flux of 12 LMH under FO using 1 M NaCl against DI water lies also in the flux range for TFC FO membranes. , …”

“…Here, we note that freestanding PA/CNM allows a significantly higher water flux (∼100 LMH, DS = 1 M NaCl) compared to state-of-the-art flatsheet thin-film composite (TFC) FO membranes, which typically demonstrate a water flux of 10−40 LMH and a salt selectivity of 0.2− 0.6 g L −1 with 1 M NaCl as the DS. 46,48 However, as with other 2D materials, 4,5,7,14,22,39,45,49,50 the membrane is fragile on the macroscopic scale and cannot be handled without a supporting layer. Depending on the support used, usually, the effective membrane area represents less than 20% of the total area.…”

Polymer Membranes as Innovative Means of Quality Restoring for Wastewater Bearing Heavy Metals

“…This process occurs due to the difference of solute concentration found in the Feed Solution (FS, low solute concentration corresponding to low osmotic pressure) and the Draw Solution (DS, high solute concentration corresponding to high osmotic pressure). In the study of Hussein, a commercial asymmetric FO membrane (cellulose triacetate (CTA)) was used for removing Cd ions from water [115,116]. Potassium chloride (KCl) solutions were used for the drawing processes.…”

“…It was also observed that the water flux decreased by increasing the operating time of the experiment, the concentration, and pH of feed solution. Overall, the FO flowing process was more efficient than the FO batch process [115,116], with higher rejection efficiency and higher water flux values.…”